(a) Field of the Invention
The present invention relates to a fuel cell, and more particularly, to a composite ceramic material electrically connecting an anode and a separation plate of a fuel cell, and a method for manufacturing the same.
(b) Description of the Related Art
Among fuel cells, if a solid oxide fuel cell (SOFC) is described as an example thereof, the fuel cell is formed of a structure where a plurality of electric generating units formed of a unit cell and a separation plate are laminated. The unit cell includes an electrolyte film, an anode (air electrode) disposed on one surface of the electrolyte film, and a cathode (fuel electrode) disposed on another surface of the electrolyte film.
If oxygen is supplied to the anode and hydrogen is supplied to the cathode, oxygen ions generated by a reduction reaction of oxygen at the anode are transported through the electrolyte film to the cathode, and then reacted with hydrogen supplied to the cathode to generate water. In this case, in the course of transporting the electrons generated at the cathode to the anode to be consumed, the electrons flow to an external circuit, and the unit cell generates consumed, the electrons flow to an external circuit, and the unit cell generates electrical energy by using the flow of electrons.
In the case of the solid oxide fuel cell, since electrical energy generated by one unit cell has a limitation, generally, a stack structure where a plurality of unit cells is laminated is formed.
In each unit cell having the stack structure, a separation plate electrically connecting the anode and the cathode and preventing gases from being mixed is generally used.
Generally, a stainless steel plate is used as the separation plate, the separation plate provides a gas flow path to the anode (air electrode) and also provides a gas flow path to the cathode (fuel electrode).
One of the methods of improving performance in the solid oxide fuel cell is to reduce electrical resistance of the stack, that is, internal resistance of the fuel cell.
To this end, a constitution where a material having excellent electric conductivity is used as the material of the separation plate and the polar plate or contact electrical resistance thereof is reduced has been proposed. An example thereof includes the case where a current collector transporting current is inserted between the anode and the separation plate and a platinum mesh (Pt mesh) is used as the current collector. Examples of another method include the case where an antioxidant metal mesh is used instead of platinum in order to reduce cost.
However, in the case where the metal material is used as the current collector, when the material is exposed to an oxidizing atmosphere over a long period of time, there is a problem in that oxides are formed on a surface thereof to increase resistance of a stack, thus deteriorating performance of the stack.
Accordingly, it is required that oxides that are stable and exhibits conductivity even in an oxidizing atmosphere are adopted to ensure stable performance even when a stack is operated over a long period of time.
A ceramic material having a perovskite structure is known as a contact material electrically connecting the polar plate and the separation plate of the fuel cell.
However, in the case of the perovskite ceramic material, physical properties of the material need to be further improved so that electrical conductivity is further improved and the material is chemically and mechanically stable.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.